include/io/channel.h

   1 /*
   2  * QEMU I/O channels
   3  *
   4  * Copyright (c) 2015 Red Hat, Inc.
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  18  *
  19  */
  20
  21 #ifndef QIO_CHANNEL_H
  22 #define QIO_CHANNEL_H
  23
  24 #include "qemu-common.h"
  25 #include "qom/object.h"
  26 #include "qemu/coroutine.h"
  27 #include "block/aio.h"
  28
  29 #define TYPE_QIO_CHANNEL "qio-channel"
  30 #define QIO_CHANNEL(obj)                                    \
  31     OBJECT_CHECK(QIOChannel, (obj), TYPE_QIO_CHANNEL)
  32 #define QIO_CHANNEL_CLASS(klass)                                    \
  33     OBJECT_CLASS_CHECK(QIOChannelClass, klass, TYPE_QIO_CHANNEL)
  34 #define QIO_CHANNEL_GET_CLASS(obj)                                  \
  35     OBJECT_GET_CLASS(QIOChannelClass, obj, TYPE_QIO_CHANNEL)
  36
  37 typedef struct QIOChannel QIOChannel;
  38 typedef struct QIOChannelClass QIOChannelClass;
  39
  40 #define QIO_CHANNEL_ERR_BLOCK -2
  41
  42 typedef enum QIOChannelFeature QIOChannelFeature;
  43
  44 enum QIOChannelFeature {
  45     QIO_CHANNEL_FEATURE_FD_PASS,
  46     QIO_CHANNEL_FEATURE_SHUTDOWN,
  47     QIO_CHANNEL_FEATURE_LISTEN,
  48 };
  49
  50
  51 typedef enum QIOChannelShutdown QIOChannelShutdown;
  52
  53 enum QIOChannelShutdown {
  54     QIO_CHANNEL_SHUTDOWN_BOTH,
  55     QIO_CHANNEL_SHUTDOWN_READ,
  56     QIO_CHANNEL_SHUTDOWN_WRITE,
  57 };
  58
  59 typedef gboolean (*QIOChannelFunc)(QIOChannel *ioc,
  60                                    GIOCondition condition,
  61                                    gpointer data);
  62
  63 /**
  64  * QIOChannel:
  65  *
  66  * The QIOChannel defines the core API for a generic I/O channel
  67  * class hierarchy. It is inspired by GIOChannel, but has the
  68  * following differences
  69  *
  70  *  - Use QOM to properly support arbitrary subclassing
  71  *  - Support use of iovecs for efficient I/O with multiple blocks
  72  *  - None of the character set translation, binary data exclusively
  73  *  - Direct support for QEMU Error object reporting
  74  *  - File descriptor passing
  75  *
  76  * This base class is abstract so cannot be instantiated. There
  77  * will be subclasses for dealing with sockets, files, and higher
  78  * level protocols such as TLS, WebSocket, etc.
  79  */
  80
  81 struct QIOChannel {
  82     Object parent;
  83     unsigned int features; /* bitmask of QIOChannelFeatures */
  84     char *name;
  85     AioContext *ctx;
  86     Coroutine *read_coroutine;
  87     Coroutine *write_coroutine;
  88 #ifdef _WIN32
  89     HANDLE event; /* For use with GSource on Win32 */
  90 #endif
  91 };
  92
  93 /**
  94  * QIOChannelClass:
  95  *
  96  * This class defines the contract that all subclasses
  97  * must follow to provide specific channel implementations.
  98  * The first five callbacks are mandatory to support, others
  99  * provide additional optional features.
 100  *
 101  * Consult the corresponding public API docs for a description
 102  * of the semantics of each callback
 103  */
 104 struct QIOChannelClass {
 105     ObjectClass parent;
 106
 107     /* Mandatory callbacks */
 108     ssize_t (*io_writev)(QIOChannel *ioc,
 109                          const struct iovec *iov,
 110                          size_t niov,
 111                          int *fds,
 112                          size_t nfds,
 113                          Error **errp);
 114     ssize_t (*io_readv)(QIOChannel *ioc,
 115                         const struct iovec *iov,
 116                         size_t niov,
 117                         int **fds,
 118                         size_t *nfds,
 119                         Error **errp);
 120     int (*io_close)(QIOChannel *ioc,
 121                     Error **errp);
 122     GSource * (*io_create_watch)(QIOChannel *ioc,
 123                                  GIOCondition condition);
 124     int (*io_set_blocking)(QIOChannel *ioc,
 125                            bool enabled,
 126                            Error **errp);
 127
 128     /* Optional callbacks */
 129     int (*io_shutdown)(QIOChannel *ioc,
 130                        QIOChannelShutdown how,
 131                        Error **errp);
 132     void (*io_set_cork)(QIOChannel *ioc,
 133                         bool enabled);
 134     void (*io_set_delay)(QIOChannel *ioc,
 135                          bool enabled);
 136     off_t (*io_seek)(QIOChannel *ioc,
 137                      off_t offset,
 138                      int whence,
 139                      Error **errp);
 140     void (*io_set_aio_fd_handler)(QIOChannel *ioc,
 141                                   AioContext *ctx,
 142                                   IOHandler *io_read,
 143                                   IOHandler *io_write,
 144                                   void *opaque);
 145 };
 146
 147 /* General I/O handling functions */
 148
 149 /**
 150  * qio_channel_has_feature:
 151  * @ioc: the channel object
 152  * @feature: the feature to check support of
 153  *
 154  * Determine whether the channel implementation supports
 155  * the optional feature named in @feature.
 156  *
 157  * Returns: true if supported, false otherwise.
 158  */
 159 bool qio_channel_has_feature(QIOChannel *ioc,
 160                              QIOChannelFeature feature);
 161
 162 /**
 163  * qio_channel_set_feature:
 164  * @ioc: the channel object
 165  * @feature: the feature to set support for
 166  *
 167  * Add channel support for the feature named in @feature.
 168  */
 169 void qio_channel_set_feature(QIOChannel *ioc,
 170                              QIOChannelFeature feature);
 171
 172 /**
 173  * qio_channel_set_name:
 174  * @ioc: the channel object
 175  * @name: the name of the channel
 176  *
 177  * Sets the name of the channel, which serves as an aid
 178  * to debugging. The name is used when creating GSource
 179  * watches for this channel.
 180  */
 181 void qio_channel_set_name(QIOChannel *ioc,
 182                           const char *name);
 183
 184 /**
 185  * qio_channel_readv_full:
 186  * @ioc: the channel object
 187  * @iov: the array of memory regions to read data into
 188  * @niov: the length of the @iov array
 189  * @fds: pointer to an array that will received file handles
 190  * @nfds: pointer filled with number of elements in @fds on return
 191  * @errp: pointer to a NULL-initialized error object
 192  *
 193  * Read data from the IO channel, storing it in the
 194  * memory regions referenced by @iov. Each element
 195  * in the @iov will be fully populated with data
 196  * before the next one is used. The @niov parameter
 197  * specifies the total number of elements in @iov.
 198  *
 199  * It is not required for all @iov to be filled with
 200  * data. If the channel is in blocking mode, at least
 201  * one byte of data will be read, but no more is
 202  * guaranteed. If the channel is non-blocking and no
 203  * data is available, it will return QIO_CHANNEL_ERR_BLOCK
 204  *
 205  * If the channel has passed any file descriptors,
 206  * the @fds array pointer will be allocated and
 207  * the elements filled with the received file
 208  * descriptors. The @nfds pointer will be updated
 209  * to indicate the size of the @fds array that
 210  * was allocated. It is the callers responsibility
 211  * to call close() on each file descriptor and to
 212  * call g_free() on the array pointer in @fds.
 213  *
 214  * It is an error to pass a non-NULL @fds parameter
 215  * unless qio_channel_has_feature() returns a true
 216  * value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
 217  *
 218  * Returns: the number of bytes read, or -1 on error,
 219  * or QIO_CHANNEL_ERR_BLOCK if no data is available
 220  * and the channel is non-blocking
 221  */
 222 ssize_t qio_channel_readv_full(QIOChannel *ioc,
 223                                const struct iovec *iov,
 224                                size_t niov,
 225                                int **fds,
 226                                size_t *nfds,
 227                                Error **errp);
 228
 229
 230 /**
 231  * qio_channel_writev_full:
 232  * @ioc: the channel object
 233  * @iov: the array of memory regions to write data from
 234  * @niov: the length of the @iov array
 235  * @fds: an array of file handles to send
 236  * @nfds: number of file handles in @fds
 237  * @errp: pointer to a NULL-initialized error object
 238  *
 239  * Write data to the IO channel, reading it from the
 240  * memory regions referenced by @iov. Each element
 241  * in the @iov will be fully sent, before the next
 242  * one is used. The @niov parameter specifies the
 243  * total number of elements in @iov.
 244  *
 245  * It is not required for all @iov data to be fully
 246  * sent. If the channel is in blocking mode, at least
 247  * one byte of data will be sent, but no more is
 248  * guaranteed. If the channel is non-blocking and no
 249  * data can be sent, it will return QIO_CHANNEL_ERR_BLOCK
 250  *
 251  * If there are file descriptors to send, the @fds
 252  * array should be non-NULL and provide the handles.
 253  * All file descriptors will be sent if at least one
 254  * byte of data was sent.
 255  *
 256  * It is an error to pass a non-NULL @fds parameter
 257  * unless qio_channel_has_feature() returns a true
 258  * value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
 259  *
 260  * Returns: the number of bytes sent, or -1 on error,
 261  * or QIO_CHANNEL_ERR_BLOCK if no data is can be sent
 262  * and the channel is non-blocking
 263  */
 264 ssize_t qio_channel_writev_full(QIOChannel *ioc,
 265                                 const struct iovec *iov,
 266                                 size_t niov,
 267                                 int *fds,
 268                                 size_t nfds,
 269                                 Error **errp);
 270
 271 /**
 272  * qio_channel_readv:
 273  * @ioc: the channel object
 274  * @iov: the array of memory regions to read data into
 275  * @niov: the length of the @iov array
 276  * @errp: pointer to a NULL-initialized error object
 277  *
 278  * Behaves as qio_channel_readv_full() but does not support
 279  * receiving of file handles.
 280  */
 281 ssize_t qio_channel_readv(QIOChannel *ioc,
 282                           const struct iovec *iov,
 283                           size_t niov,
 284                           Error **errp);
 285
 286 /**
 287  * qio_channel_writev:
 288  * @ioc: the channel object
 289  * @iov: the array of memory regions to write data from
 290  * @niov: the length of the @iov array
 291  * @errp: pointer to a NULL-initialized error object
 292  *
 293  * Behaves as qio_channel_writev_full() but does not support
 294  * sending of file handles.
 295  */
 296 ssize_t qio_channel_writev(QIOChannel *ioc,
 297                            const struct iovec *iov,
 298                            size_t niov,
 299                            Error **errp);
 300
 301 /**
 302  * qio_channel_readv:
 303  * @ioc: the channel object
 304  * @buf: the memory region to read data into
 305  * @buflen: the length of @buf
 306  * @errp: pointer to a NULL-initialized error object
 307  *
 308  * Behaves as qio_channel_readv_full() but does not support
 309  * receiving of file handles, and only supports reading into
 310  * a single memory region.
 311  */
 312 ssize_t qio_channel_read(QIOChannel *ioc,
 313                          char *buf,
 314                          size_t buflen,
 315                          Error **errp);
 316
 317 /**
 318  * qio_channel_writev:
 319  * @ioc: the channel object
 320  * @buf: the memory regions to send data from
 321  * @buflen: the length of @buf
 322  * @errp: pointer to a NULL-initialized error object
 323  *
 324  * Behaves as qio_channel_writev_full() but does not support
 325  * sending of file handles, and only supports writing from a
 326  * single memory region.
 327  */
 328 ssize_t qio_channel_write(QIOChannel *ioc,
 329                           const char *buf,
 330                           size_t buflen,
 331                           Error **errp);
 332
 333 /**
 334  * qio_channel_set_blocking:
 335  * @ioc: the channel object
 336  * @enabled: the blocking flag state
 337  * @errp: pointer to a NULL-initialized error object
 338  *
 339  * If @enabled is true, then the channel is put into
 340  * blocking mode, otherwise it will be non-blocking.
 341  *
 342  * In non-blocking mode, read/write operations may
 343  * return QIO_CHANNEL_ERR_BLOCK if they would otherwise
 344  * block on I/O
 345  */
 346 int qio_channel_set_blocking(QIOChannel *ioc,
 347                              bool enabled,
 348                              Error **errp);
 349
 350 /**
 351  * qio_channel_close:
 352  * @ioc: the channel object
 353  * @errp: pointer to a NULL-initialized error object
 354  *
 355  * Close the channel, flushing any pending I/O
 356  *
 357  * Returns: 0 on success, -1 on error
 358  */
 359 int qio_channel_close(QIOChannel *ioc,
 360                       Error **errp);
 361
 362 /**
 363  * qio_channel_shutdown:
 364  * @ioc: the channel object
 365  * @how: the direction to shutdown
 366  * @errp: pointer to a NULL-initialized error object
 367  *
 368  * Shutdowns transmission and/or receiving of data
 369  * without closing the underlying transport.
 370  *
 371  * Not all implementations will support this facility,
 372  * so may report an error. To avoid errors, the
 373  * caller may check for the feature flag
 374  * QIO_CHANNEL_FEATURE_SHUTDOWN prior to calling
 375  * this method.
 376  *
 377  * Returns: 0 on success, -1 on error
 378  */
 379 int qio_channel_shutdown(QIOChannel *ioc,
 380                          QIOChannelShutdown how,
 381                          Error **errp);
 382
 383 /**
 384  * qio_channel_set_delay:
 385  * @ioc: the channel object
 386  * @enabled: the new flag state
 387  *
 388  * Controls whether the underlying transport is
 389  * permitted to delay writes in order to merge
 390  * small packets. If @enabled is true, then the
 391  * writes may be delayed in order to opportunistically
 392  * merge small packets into larger ones. If @enabled
 393  * is false, writes are dispatched immediately with
 394  * no delay.
 395  *
 396  * When @enabled is false, applications may wish to
 397  * use the qio_channel_set_cork() method to explicitly
 398  * control write merging.
 399  *
 400  * On channels which are backed by a socket, this
 401  * API corresponds to the inverse of TCP_NODELAY flag,
 402  * controlling whether the Nagle algorithm is active.
 403  *
 404  * This setting is merely a hint, so implementations are
 405  * free to ignore this without it being considered an
 406  * error.
 407  */
 408 void qio_channel_set_delay(QIOChannel *ioc,
 409                            bool enabled);
 410
 411 /**
 412  * qio_channel_set_cork:
 413  * @ioc: the channel object
 414  * @enabled: the new flag state
 415  *
 416  * Controls whether the underlying transport is
 417  * permitted to dispatch data that is written.
 418  * If @enabled is true, then any data written will
 419  * be queued in local buffers until @enabled is
 420  * set to false once again.
 421  *
 422  * This feature is typically used when the automatic
 423  * write coalescing facility is disabled via the
 424  * qio_channel_set_delay() method.
 425  *
 426  * On channels which are backed by a socket, this
 427  * API corresponds to the TCP_CORK flag.
 428  *
 429  * This setting is merely a hint, so implementations are
 430  * free to ignore this without it being considered an
 431  * error.
 432  */
 433 void qio_channel_set_cork(QIOChannel *ioc,
 434                           bool enabled);
 435
 436
 437 /**
 438  * qio_channel_seek:
 439  * @ioc: the channel object
 440  * @offset: the position to seek to, relative to @whence
 441  * @whence: one of the (POSIX) SEEK_* constants listed below
 442  * @errp: pointer to a NULL-initialized error object
 443  *
 444  * Moves the current I/O position within the channel
 445  * @ioc, to be @offset. The value of @offset is
 446  * interpreted relative to @whence:
 447  *
 448  * SEEK_SET - the position is set to @offset bytes
 449  * SEEK_CUR - the position is moved by @offset bytes
 450  * SEEK_END - the position is set to end of the file plus @offset bytes
 451  *
 452  * Not all implementations will support this facility,
 453  * so may report an error.
 454  *
 455  * Returns: the new position on success, (off_t)-1 on failure
 456  */
 457 off_t qio_channel_io_seek(QIOChannel *ioc,
 458                           off_t offset,
 459                           int whence,
 460                           Error **errp);
 461
 462
 463 /**
 464  * qio_channel_create_watch:
 465  * @ioc: the channel object
 466  * @condition: the I/O condition to monitor
 467  *
 468  * Create a new main loop source that is used to watch
 469  * for the I/O condition @condition. Typically the
 470  * qio_channel_add_watch() method would be used instead
 471  * of this, since it directly attaches a callback to
 472  * the source
 473  *
 474  * Returns: the new main loop source.
 475  */
 476 GSource *qio_channel_create_watch(QIOChannel *ioc,
 477                                   GIOCondition condition);
 478
 479 /**
 480  * qio_channel_add_watch:
 481  * @ioc: the channel object
 482  * @condition: the I/O condition to monitor
 483  * @func: callback to invoke when the source becomes ready
 484  * @user_data: opaque data to pass to @func
 485  * @notify: callback to free @user_data
 486  *
 487  * Create a new main loop source that is used to watch
 488  * for the I/O condition @condition. The callback @func
 489  * will be registered against the source, to be invoked
 490  * when the source becomes ready. The optional @user_data
 491  * will be passed to @func when it is invoked. The @notify
 492  * callback will be used to free @user_data when the
 493  * watch is deleted
 494  *
 495  * The returned source ID can be used with g_source_remove()
 496  * to remove and free the source when no longer required.
 497  * Alternatively the @func callback can return a FALSE
 498  * value.
 499  *
 500  * Returns: the source ID
 501  */
 502 guint qio_channel_add_watch(QIOChannel *ioc,
 503                             GIOCondition condition,
 504                             QIOChannelFunc func,
 505                             gpointer user_data,
 506                             GDestroyNotify notify);
 507
 508
 509 /**
 510  * qio_channel_attach_aio_context:
 511  * @ioc: the channel object
 512  * @ctx: the #AioContext to set the handlers on
 513  *
 514  * Request that qio_channel_yield() sets I/O handlers on
 515  * the given #AioContext.  If @ctx is %NULL, qio_channel_yield()
 516  * uses QEMU's main thread event loop.
 517  *
 518  * You can move a #QIOChannel from one #AioContext to another even if
 519  * I/O handlers are set for a coroutine.  However, #QIOChannel provides
 520  * no synchronization between the calls to qio_channel_yield() and
 521  * qio_channel_attach_aio_context().
 522  *
 523  * Therefore you should first call qio_channel_detach_aio_context()
 524  * to ensure that the coroutine is not entered concurrently.  Then,
 525  * while the coroutine has yielded, call qio_channel_attach_aio_context(),
 526  * and then aio_co_schedule() to place the coroutine on the new
 527  * #AioContext.  The calls to qio_channel_detach_aio_context()
 528  * and qio_channel_attach_aio_context() should be protected with
 529  * aio_context_acquire() and aio_context_release().
 530  */
 531 void qio_channel_attach_aio_context(QIOChannel *ioc,
 532                                     AioContext *ctx);
 533
 534 /**
 535  * qio_channel_detach_aio_context:
 536  * @ioc: the channel object
 537  *
 538  * Disable any I/O handlers set by qio_channel_yield().  With the
 539  * help of aio_co_schedule(), this allows moving a coroutine that was
 540  * paused by qio_channel_yield() to another context.
 541  */
 542 void qio_channel_detach_aio_context(QIOChannel *ioc);
 543
 544 /**
 545  * qio_channel_yield:
 546  * @ioc: the channel object
 547  * @condition: the I/O condition to wait for
 548  *
 549  * Yields execution from the current coroutine until the condition
 550  * indicated by @condition becomes available.  @condition must
 551  * be either %G_IO_IN or %G_IO_OUT; it cannot contain both.  In
 552  * addition, no two coroutine can be waiting on the same condition
 553  * and channel at the same time.
 554  *
 555  * This must only be called from coroutine context
 556  */
 557 void qio_channel_yield(QIOChannel *ioc,
 558                        GIOCondition condition);
 559
 560 /**
 561  * qio_channel_wait:
 562  * @ioc: the channel object
 563  * @condition: the I/O condition to wait for
 564  *
 565  * Block execution from the current thread until
 566  * the condition indicated by @condition becomes
 567  * available.
 568  *
 569  * This will enter a nested event loop to perform
 570  * the wait.
 571  */
 572 void qio_channel_wait(QIOChannel *ioc,
 573                       GIOCondition condition);
 574
 575 /**
 576  * qio_channel_set_aio_fd_handler:
 577  * @ioc: the channel object
 578  * @ctx: the AioContext to set the handlers on
 579  * @io_read: the read handler
 580  * @io_write: the write handler
 581  * @opaque: the opaque value passed to the handler
 582  *
 583  * This is used internally by qio_channel_yield().  It can
 584  * be used by channel implementations to forward the handlers
 585  * to another channel (e.g. from #QIOChannelTLS to the
 586  * underlying socket).
 587  */
 588 void qio_channel_set_aio_fd_handler(QIOChannel *ioc,
 589                                     AioContext *ctx,
 590                                     IOHandler *io_read,
 591                                     IOHandler *io_write,
 592                                     void *opaque);
 593
 594 #endif /* QIO_CHANNEL_H */